[Serf27]

I pulled the plugs again today and re gapped them to .42/3

Added dielectric grease to the coils
Cleaned pre cat bank1 & 2 connectors.
Removed air box and put it back on to make sure everything was tight.
Cleaned MAF from every angle.
Removed DME connectors and no visual issues there.


Drove the car for 45 minutes, in the same driving pattern I’ve been using to try and trigger the codes or get monitors ready.

No codes the entire time. Nothing would ready up.
I let the engine idle for a few minutes after, O2 Heater got ready, code came back for
2CB6-Bank1 post cat/sensor2 stuck lean.
2C7E- bank1 too rich.

THE CODES CAME UP AFTER 45 min drive time.
They would always come up within 1-3 minutes.

Changed the MAF to a known good one and cleared the codes.
The same 2 codes came up after about 7 minutes.
Fuel trims are now at

-3.17 LTFT(B1)
3.46 LTFT(B2)

.01 STFT(B1)
.04 STFT(B2)

——

The codes do not pop up almost instantly now.
The 2 key differences from now and before is:
Outside temperature dropped 7°F.
Plugs have been re gapped.

Could it be that the plugs are delaying the codes from returning? IE: Put new plugs?

The fault strategy for both codes is the same.
Check plugs/wiring:

-Plugs look ok, no misfires under and cruising/WOT.


Electrical test wiring:
-Post cat chassis connectors showed everything was fine.

Check for leaks downstream of post cat sensor:
-I don’t have a smoke machine so I either replace those Dow pipe gaskets or move forward.

Replace post cat bank 1 sensor:

Replace pre cat bank 1 sensor:

So I either try new plugs, change the Dow pipe gaskets first or go after the O2 sensors.

Is this what is happening, the post cat O2 sensor is “signal fixed lean”
And the pre cat tries to compensate but ends up running too rich?

Here’s the Fuel trims with the different MAF installed at low rpm and higher rpm.

Thanks.

[Sgop335]

Originally Posted by Serf27

Be prepared for what if adaptions are reset?
Just fact the stft is slow to come back and may take a sleep cycle to come back
When mhd is used to reset fuel adaptations only stft comes back quickly.

The LTFT are far off as in 1 is negative and the other is positive? Yes
Or they are 13% away from each other? Yes

Their high delta is pointing to something

Thanks.

..

[Andystobbs]

What kind of stupid app is that? First two rows are arranged
B1, B2
Then the third is
B2, B1.

Unplug post cat B1 and see how the fuel trim responds. Drive around for a bit.

[PhaseP]

Originally Posted by gbalthrop

Where & How does the 4-wire sensor used in N52 engine get this "Reference" reading of oxygen in the "air".

As far as I know all lambda 02 sensors work by comparing (referencing) ambient air oxgen to oxygen level inside the exhaust. The post cat 02 sensors at N52 are narrow band sensors. The pre-cat 02 sensors are wide band sensors. The narrow band sensors generate a voltage based on the amount of difference oxygen between outside air and air inside exhaust.

The wide band sensors generate a current based on that same inside exhaust air and outside air, to my knowledge. They are able to give a current reading that corresponds to oxygen percentage but still based on air outside. The narrow band is like trinary output, too much oxygen inside exhaust, too little oxygen inside exhaust, and expected oxygen inside exhaust compared to outside air.
When exhaust leaks near 02 sensor, the outside air it uses gets polluted for it to use as a good reference.
I gave the wiki as easy reference.

"I did NOT see any footnote in the Wiki- article that relates to that quoted statement"

There are multiple places and depictions where the wiki article mentions the sensor has a side to externail air, and a side to exhaust air and this is how they work. Wiki is not the only source with that information.

I still have my original O2 sensors. I had O2 sensor code when my exhaust connection at the flange started to leak. Fixed that, code is gone.

I am not saying it applies to the OP's case though.

[PhaseP]

Originally Posted by Serf27

Check for leaks downstream of post cat sensor:
-I don’t have a smoke machine so I either replace those Dow pipe gaskets or move forward.

You don't need a smoke machine for that. If there is leak, there will be some visible black soot there it leaks. You would also hear some exhaust note in the leak. In my case where the gasket at flanges leaked, I was getting loud blown exhaust note when that connection got wet while driving in rain. Once the gasket and connection dried, that loud exhaust note was going away.

[PhaseP]

About the outside air being used as reference by 02 sensors, the wiki has this information too, which is odd to me. I always used to think the sensor is using some section of it that is to outside as reference air. This says it gets that reference air all the way from the other end of the cables. Don't know. All I know for sure is, when I fixed my leaking exhaust flange, my 02 code was gone:

"In automotive applications the titania sensor, unlike the zirconia sensor, does not require a reference sample of atmospheric air to operate properly. This makes the sensor assembly easier to design against water contamination. While most automotive sensors are submersible, zirconia-based sensors require a very small supply of reference air from the atmosphere. In theory, the sensor wire harness and connector are sealed. Air that leaches through the wire harness to the sensor is assumed to come from an open point in the harness – usually the ECU, which is housed in an enclosed space like the trunk or vehicle interior."

https://en.wikipedia.org/wiki/Oxygen_sensor

[Serf27]

The app is protools.
I had the gauges set up like that. I’ll re arrange them so it’s better to read.

I’ll change the gaskets on the flanges today.

If no success, I’ll post readings of fuel trims with bank 1 disconnected.

I’ll then replace bank1 post cat sensor.

Thanks all.

[Serf27]

Auto parts store didn’t have both gaskets, and because of a bracket holding the exhaust together, I couldn’t just change one, possibly causing a leak on Bank2 for re using the gasket.

BUTTTT! The bank1 post cat sensor was the issue.

The new one instantly showed .7V on start up, which matched Bank2 sensor.

I am guessing the old sensor was internally shorting out(as someone previously said) or working intermittently.
Even though when it did work, it only got up to .4V, the DME didn’t like that .3V difference, or sensed something was wrong when the sensor would drop down to/stay at 0V.

0V must mean lean? So pre cat was trying to compensate with more fuel, giving the other code “too rich”.
and when the DME constantly saw 0V, it triggered bank 1 stuck lean and too rich?

That’s just what I think, I don’t know.
I did the drive cycle, all monitors ready and no more codes.

Thanks a bunch to everyone that helped!

[gbalthrop]

Originally Posted by PhaseP

As far as I know all lambda 02 sensors work by comparing (referencing) ambient air oxgen to oxygen level inside the exhaust. The post cat 02 sensors at N52 are narrow band sensors. The pre-cat 02 sensors are wide band sensors. The narrow band sensors generate a voltage based on the amount of difference oxygen between outside air and air inside exhaust.
The wide band sensors generate a current based on that same inside exhaust air and outside air, to my knowledge. They are able to give a current reading that corresponds to oxygen percentage but still based on air outside. The narrow band is like trinary output, too much oxygen inside exhaust, too little oxygen inside exhaust, and expected oxygen inside exhaust compared to outside air.
When exhaust leaks near 02 sensor, the outside air it uses gets polluted for it to use as a good reference.
I gave the wiki as easy reference.

There are multiple places and depictions where the wiki article mentions the sensor has a side to externail air, and a side to exhaust air and this is how they work. Wiki is not the only source with that information...

Originally Posted by PhaseP

About the outside air being used as reference by 02 sensors, the wiki has this information too, which is odd to me. I always used to think the sensor is using some section of it that is to outside as reference air. This says it gets that reference air all the way from the other end of the cables. Don't know. All I know for sure is, when I fixed my leaking exhaust flange, my 02 code was gone:

"In automotive applications the titania sensor, unlike the zirconia sensor, does not require a reference sample of atmospheric air to operate properly. This makes the sensor assembly easier to design against water contamination. While most automotive sensors are submersible, zirconia-based sensors require a very small supply of reference air from the atmosphere. In theory, the sensor wire harness and connector are sealed. Air that leaches through the wire harness to the sensor is assumed to come from an open point in the harness – usually the ECU, which is housed in an enclosed space like the trunk or vehicle interior."
https://en.wikipedia.org/wiki/Oxygen_sensor

Please understand I appreciate your "Engineering approach" and search for proper explanation. I was NOT complaining about your approach (which I share). Rather I was "Observing" (Ranting?) about lack of sufficiently-detailed information online, such as WHERE does BMW O2 Sensor get "Reference Air", particularly since "Serf27" indicated he may have adversely affected Post-Cat sensor performance by spraying contact cleaner on connector pins & sockets some distance away from sensor itself.

Sorry for "Hi-Jacking" your thread Serf27.

Everything I have read so far confirms what you report above. My concern is that I CANNOT find what I would deem Clear, Reliable information on HOW the E9x Pre-cat and Post-cat Sensors work, if they are Wide/Narrow Band, Zirconia/ Titania/ Other, WHERE they get Reference air (IF used), etc.

ISTA states NOT to spray BMW brand Contact Cleaner on O2 sensor OR ITS CONNECTOR, without elaboration on how spray on connector could affect sensor function.

Here is one of the few meaningful Bosch articles on the subject which I have found thus far. Note that the "Product Details of Lambda Sensor" do NOT show (to me, at least ;-) WHERE the Reference Air comes from, although it appears that the E Sensor Element is open to some degree at the "wiring end" of the sensor:
https://www.bosch-mobility-solutions...lambda-sensor/

ANYONE bought Either Pre-/Post- Cat Sensors recently, who can indicate Make/ model/ part# of sensor and WHAT documentation was "in the box" by way of installation/handling instructions, or any substances to avoid using around the sensor?

I can appreciate the Manufacturer's desire to (1) Prevent "piracy" of technology, & (2) Promote Sales. However that leads to treating customers (US) like idiots and NOT providing enough information for knowledgeable use of the product. At its extreme, the concept of "Intellectual Property" means: "What's MINE is MINE, and what's YOURS is NEGOTIABLE".

FIFTEEN (15) years after Bosch made our O2 Sensors, do they REALLY have any reason to prevent a competitor (much less the ultimate consumer -- US) from knowing how the product was made and HOW it Functions? Seems like senseless "NON-Disclosure" to me.
Here endeth the Rant,
George

[gbalthrop]

Originally Posted by Serf27

BUTTTT! The bank1 post cat sensor was the issue. The new one instantly showed .7V on start up, which matched Bank2 sensor.
I did the drive cycle, all monitors ready and no more codes...

All's Swell that ends Swell! Just to recap my simplified "Summary" of issue:
2C7E-Oxygen sensor control
2C6B-Oxygen sensor after catalytic converter-System check
Fault Information Sheet (LINK) for 2C7E Fault Code (Primary):
https://bmwfault.codes/XMLDiagView?d...gAMAA5ADAANAA=
BTW, "4. Visual inspection of wiring and plugs" -- "Plugs" should PROBABLY mean Connector Pins & Sockets, NOT Spark Plugs

Live Data Voltage: Voltage Lambda Probe Behind Cat 1: 0V at idle/revving

FIXED by replacement of Post-Cat Bank 1 O2 Sensor.

Questions:
1) Was something sprayed on that O2 sensor element, OR on its connector?
2) If so, what was sprayed on which portion of the Sensor?

Bonus Question:
What Brand Sensor was replacement, and was there ANYTHING in box that related to Cautions in Installation or Use, such as do NOT spray with contact cleaner, drop, expose to silicone, oil, etc.?

Thanks,
George

[PhaseP]

Originally Posted by gbalthrop

Sorry for "Hi-Jacking" your thread Serf27.

+1, but I am shamelessly continuing on the hijack

Everything I have read so far confirms what you report above. My concern is that I CANNOT find what I would deem Clear, Reliable information on HOW the E9x Pre-cat and Post-cat Sensors work, if they are Wide/Narrow Band, Zirconia/ Titania/ Other, WHERE they get Reference air (IF used), etc.

Here you go: https://www.boschautoparts.com/docum...ech%20Tips.pdf

So wiki was right, at least for Bosch O2 sensors, they pull the ambient air from the wires. I would have never guessed, it is like black magic.

It is from this page, and under "Support" button : https://www.boschautoparts.com/p/uni...gen-o2-sensors

There is a trade brochure link there, which also states the same about ambient air pulled through wires, but goes into a bit more detail in the sensor types.

About the types of sensors, I had matched the BMW part numbers at ECS tuning with Bosch part numbers for the O2 sensors. Then had searched those part numbers at Bosch's web site. And the pre-cat O2 sensors came out to be wide-band, and post-cat narrow band. I had read about same before but don't remember exactly where, probably in this forum

[Andystobbs]

There's no big conspiracy to keep lambda sensor info secret. The Internet is packed with info on nernst cells.

As for telling them apart, NB has 4 wires. WB has at least 5

[gbalthrop]

Originally Posted by PhaseP

+1, but I am shamelessly continuing on the hijack [Serf27 solved his issue, so we can now "OPENLY DEBATE" why spraying contact cleaner on the connector can damage the Sensor Element.] Here you go: https://www.boschautoparts.com/docum...ech%20Tips.pdf
So wiki was right, at least for Bosch O2 sensors, they pull the ambient air from the wires...

Thanks for continuing to look for THE FACTS. As I read the "Tech Tips" you linked, it clearly states:

"Bosch Oxygen Sensors are the only sensors that draw their reference air from
the connector and through the wire harness to ensure the reference air
sample is clean."

So in Serf27's case, failure to warn of that "Nifty little Sales Point" caused him to trash a ~$100 Sensor by spraying contact cleaner on the connector pins/sockets. I would have done the SAME thing if I had occasion to disconnect mine. I had NO IDEA either, and so stated earlier in this thread.

I do NOT maintain there is some "big conspiracy" related to O2 Sensor Design "Non-Disclosure". However, my position is that in virtually EVERY trade or business, the tendency is to NOT "give away the ranch". Every major corporation and most small ones try to "Regulate" release of information regarding the Product, with careful evaluation of just what information should be in Sales & Marketing releases & ads. Pharma is about the only trade that warns of "Complications" or adverse affects of use of a particular product, largely due to requirements to do so in Government Regulations.

Of course Regulations can also make us "Numb". CA Proposition 65 basically requires a warning that the State of California has determined EVERYTHING can cause Cancer.

Your first link was titled "Bosch Tech Tips". Look at the content and see if a more apt title would have been "Bosch Marketing Talking Points". I don't see any warnings or negative substance at all. There are 6 examples/ photos in the "Oxygen Sensor Diagnosis Guide" on right of "Tips" page. Each has same "Measure": Replace the Oxygen Sensor (with Bosch of course ;-)

We've gotten so numb to the shameless marketing with subtle (at best) misrepresentation of what we are actually being exposed to, that we don't even realize how we're being "played": Hurry, limited offer, act NOW! (don't stop and think or analyze ;-).

To put a positive spin on this:
Thanks for digging for this information. I would have NEVER known and would have trashed Sensors (if I ever actually had to work on my car ;-)
Hope we ALL learned something. Maybe Government Regulation isn't "All Bad"??? C'mon 'publicans: have a sense of HUMOR.
George

[Andystobbs]

Spraying contact cleaner - or anything else - in the vicinity of the connector isn't going to ruin the sensor.

[Serf27]

Originally Posted by gbalthrop

All's Swell that ends Swell! Just to recap my simplified "Summary" of issue:
2C7E-Oxygen sensor control
2C6B-Oxygen sensor after catalytic converter-System check
Fault Information Sheet (LINK) for 2C7E Fault Code (Primary):
https://bmwfault.codes/XMLDiagView?d...gAMAA5ADAANAA=
BTW, "4. Visual inspection of wiring and plugs" -- "Plugs" should PROBABLY mean Connector Pins & Sockets, NOT Spark Plugs

Live Data Voltage: Voltage Lambda Probe Behind Cat 1: 0V at idle/revving

FIXED by replacement of Post-Cat Bank 1 O2 Sensor.

Questions:
1) Was something sprayed on that O2 sensor element, OR on its connector?
2) If so, what was sprayed on which portion of the Sensor?

Bonus Question:
What Brand Sensor was replacement, and was there ANYTHING in box that related to Cautions in Installation or Use, such as do NOT spray with contact cleaner, drop, expose to silicone, oil, etc.?

Thanks,
George

I was thinking “why is it asking to check for plugs and wiring?”
I haven’t worked on a car with plugs and wires in a few years, (distributor) LOL!

I used CRC electric cleaner and sprayed the chassis and sensor connectors.
Remember, this was to try and remedy a Bank2 post cat error. I figured, I’m cleaning Bank2, I might as well clean bank1.

I didn’t blow the connectors out with air but left them unconnected for a few seconds to allow the cleaner to evaporate.
It was either a big coincidence that the sensor failed as soon as Bank2 sensor was replaced, or the cleaner did something.

I’ll also add that I used the cleaner on pre cat connectors and MAF connectors too, but I let those sit for about a minute to allow the cleaner to completely dry out.


I got a Bosch 16414 sensor from autozone. Some ~$150!
No directions on the box and no info sheet. Only a cap over the sensor tip and some anti seize grease on the threads.

[PhaseP]

Originally Posted by Andystobbs

Spraying contact cleaner - or anything else - in the vicinity of the connector isn't going to ruin the sensor.

Well Bosch's "Tech Tips" pdf which I linked in one of the posts above says not to use dialectric grease at the connector contacts . I know contact cleaner is not dialectric grease. But Bentley manual says not to use any "Stabilant 22A" on O2 sensor connections. Looking up Stabilant 22A brings up this: https://wurthusa.com/Chemical-Produc...5-ml/p/0893622

It says it is a "contact enhancer" that leaves "a thin polymer film".
If the particular electrical contact cleaner used on the connector pins leaves similar polymer film, it would also effect those Bosch O2 sensors not work well.

[Serf27]

How is the film removed?
Maybe it caused poor contact between the connections?

[gbalthrop]

Originally Posted by PhaseP

... Bentley manual says not to use any "Stabilant 22A" on O2 sensor connections...

Thanks for the Bentley reference re Stabilant 22A. I KNEW I had read that somewhere, and "MIS-remembered" that I
saw that in ISTA, and could NOT remember the name of the Product. BTW, search of either Stabilant or 22A in ISTA: NO Hits

Well, proceeding further down the "conspiracy theory Rabbit Hole"
Attached is ScreenPrint from Bentley Manual, 003-22, which shows exactly what you say, without any explanation: WHY?
Enquiring minds want to know:
1) Does Stabilant 22A (or CRC Contact Cleaner) damage the "Element" in an O2 Sensor, and if so, HOW Quickly after use?
1a) What is the Chemical ingredient in Stabile 22A causing this warning, and does CRC Cleaner have SAME/Similar Ingredient?
2) Does Stabilant change the Resistance of the connector sufficiently to cause a signal issue?
3) NOTE: that the Bentley Manual also warns against use on "SRS Connectors", which in broadest sense means ANY connector
in the Supplemental Restraint System, but presumably is particularly applicable to Ignition Circuit connectors (the triggers),
where resistance is measured to .01 Ohm accuracy (INPA). Once again, NO explanation and "Enquiring Minds" are left to wander.

Guess all we can do is avoid chemical cleaning of O2 Sensor & SRS connectors, and live in Blissful IGNORANCE.
Thanks again,
George

[Serf27]

Here is somewhat of a diagnostic procedure/fault strategy for post/behind cat sensors. Similar to the fault strategy in post 6 of this thread, but with more info.
I didn’t go far into diagnosing some of these steps because I didn’t need to, but I’ll try to help.

1) Visual inspection of plugs and wires on sensors:
Are any of the 4 wires on the sensor ripped or damaged?
Are the plugs(connectors) fully seated within each other?
Is there any oil inside the connectors?
Are the pins in the connectors dirty?

-Clean pins and connectors at your own risk.
-Repair any damaged wires on the sensors as needed.


2)Electrical check of wiring: Turn key on/accessory on.
Using a voltmeter for all steps, tough negative lead to chassis ground and positive lead to pins on chassis connector that are being tested.

Disconnect the chassis connector from the sensor connector.
Testing sensor heater wire-Pin 1, orange wire:
Is there 12V?
Yes? Cont.
Note at this point, I had voltage.
No? Check that fuse for sensor heater is not blown.
Inspect wiring between connector and DME/inspect DME.

Testing DME to sensor signal wire voltage-Pin 4 yellow wire:
Is there .4V?
Yes? Cont.
Note at this point, I had voltage, so I continued.
No? Inspect wiring between connector and DME/inspect DME.

Testing Gray/White wire on connector-Pin 2, gray/white wire:
Note I’m not sure what this wire does, but it has voltage.
Is there 4V?
Yes? Cont.
Note at this point, I had voltage, so I continued.
No? Inspect wiring between connector and DME/inspect DME.

Testing sensor to DME return signal wire-Pin 3
Plug chassis connector into sensor connector.
Start vehicle and back probe Pin 3 on connector. Depending on which connector you test, they will be different colors.
Note: I do not know the specific voltage that is needed here. I know a good sensor reads .7V-.8V and my fault sensor was reading 0V-.4V. I also did not test this wire with the meter, with a scan tool I was able to see voltage.

Is there .7V-.8V?
Yes? Inspect wiring between connector and DME.
No? Cont.

Check exhaust system forward of downstream (post- cat) 02 sensor for leaks
If there are any leaks, it can mess with sensor output voltage that was just tested.
Is there any leaks? As mentioned above, the exhaust flange gaskets can leak.
Yes? Fix leaks as needed.
No? Replace post cat sensor.

Does error code go away?
No? Replace pre cat sensor.

Does error go away?
No? Replace control module.

Well, hope that makes sense.

[Andystobbs]

I think there is confusion here between air migrating down the actual wires vs the outer harness.